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How to Fix the “List index out of range” Error in Python

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At many points in your Python programming career, you’re going to run into the “List index out of range” error while writing your programs. What does this mean, and how do we fix this error? We’ll answer that question in this article.

The short answer is: this error occurs when you’re trying to access an item outside of your list’s range. The long answer, on the other hand, is much more interesting. To get there, we’ll learn a lot about how lists work, how to index things the bad way and the good way, and finally how to solve the above-mentioned error.

This article is aimed at Python beginners who have little experience in programming. Understanding this error early will save you plenty of time down the road. If you’re looking for some learning material, our Python Basics track includes 3 interactive courses bundled together to get you on your feet.

Indexing Python Lists

Lists are one of the most useful data structures in Python. And they come with a whole bunch of useful methods . Other Python data structures include tuples, arrays, dictionaries, and sets, but we won’t go into their details here. For hands-on experience with these structures, we have a Python Data Structures in Practice course which is suitable for beginners.

A list can be created as follows:

Instead of using square brackets ([]) to define your list, you can also use the list() built-in function.

There are already a few interesting things to note about the above example. First, you can store any data type in a list, such as an integer, string, floating-point number, or even another list. Second, the elements don’t have to be unique: the integer 1 appears twice in the above example.

The elements in a list are indexed starting from 0. Therefore, to access the first element, do the following:

Our list contains 6 elements, which you can get using the len() built-in function. To access the last element of the list, you might naively try to do the following:

This is equivalent to print(x[len(x)]) . Since list indexing starts from 0, the last element has index len(x)–1 . When we try to access the index len(x) , we are outside the range of the list and get the error. A more robust way to get the final element of the list looks like this:

While this works, it’s not the most pythonic way. A better method exploits a nice feature of lists – namely, that they can be indexed from the end of the list by using a negative number as the index. The final element can be printed as follows:

The second last element can be accessed with the index -2, and so on. This means using the index -6 will get back to the first element. Taking it one step further:

Notice this asymmetry. The first error was trying to access the element after the last with the index 6, and the second error was trying to access the element before the first with the index -7. This is due to forward indexing starting at 0 (the start of the list), and backwards indexing starting at -1 (the end of the list). This is shown graphically below:

Looping Through Lists

Whenever you’re working with lists, you’ll need to know about loops. A loop allows you to iterate through all the elements in a list.

The first type of loop we’ll take a look at is the while loop. You have to be a little more careful with while loops, because a small mistake will make them run forever, requiring you to force the program to quit. Once again, let’s try to naively loop through our list:

In this example we define our index, i , to start from zero. After every iteration of our while loop, we print the list element and then go to the next index with the += assignment operator. (This is a neat little trick, which is like doing i=i+1 .)

By the way, if you forget the final line, you’ll get an infinite loop.

We encountered the index error for the same reason as in the first section – the final element has index len(x)-1 . Just modify the condition of the while statement to reflect this, and it will work without problems.

Most of your looping will be done with a for loop, which we’ll now turn our attention to. A better method to loop through the elements in our list without the risk of running into the index error is to take advantage of the range() built-in function. This takes three arguments, of which only the stop argument is required. Try the following:

The combination of the range() and len() built-in functions takes care of worrying about when to stop indexing our list to avoid the index out of range error entirely. This method, however, is only useful if you care about knowing what the index is.

For example, maybe you want to print out the index and the element. In that case, all you need to do is modify the print() statement to print(i, x[i]) . Try doing this for yourself to see the result. Alternatively, you can use The enumerate() function in Python.

If you just want to get the element, there’s a simpler way that’s much more intuitive and readable. Just loop through the elements of the list directly:

If the user inputs an index outside the range of the list (e.g. 6), they’ll run into the list index error again. We can modify the function to check the input value with an if statement:

Doing this prevents our program from crashing if the index is out of range. You can even use a negative index in the above function.

There are other ways to do error handling in Python that will help you avoid errors like “list index out of range”. For example, you could implement a try-exceptaa block instead of the if-else statement.

To see a try-except block in action, let’s handle a potential index error in the get_value() function we wrote above. Preventing the error looks like this:

As you can probably see, the second method is a little more concise and readable. It’s also less error-prone than explicitly checking the input index with an if-else statement.

Master the “List index out of range” Error in Python

You should now know what the index out of range error in Python means, why it pops up, and how to prevent it in your Python programs.

A useful way to debug this error and understand how your programs are running is simply to print the index and compare it to the length of your list.

This error could also occur when iterating over other data structures, such as arrays, tuples, or even when iterating through a string. Using strings is a little different from  using lists; if you want to learn the tools to master this topic, consider taking our Working with Strings in Python course. The skills you learnt here should be applicable to many common use cases.

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IndexError: list assignment index out of range in Python

Last updated: Apr 8, 2024 Reading time · 9 min

# Table of Contents

• IndexError: list assignment index out of range
• (CSV) IndexError: list index out of range
• sys.argv[1] IndexError: list index out of range
• IndexError: pop index out of range

Make sure to click on the correct subheading depending on your error message.

# IndexError: list assignment index out of range in Python

The Python "IndexError: list assignment index out of range" occurs when we try to assign a value at an index that doesn't exist in the list.

To solve the error, use the append() method to add an item to the end of the list, e.g. my_list.append('b') .

Here is an example of how the error occurs.

The list has a length of 3 . Since indexes in Python are zero-based, the first index in the list is 0 , and the last is 2 .

Trying to assign a value to any positive index outside the range of 0-2 would cause the IndexError .

# Adding an item to the end of the list with append()

If you need to add an item to the end of a list, use the list.append() method instead.

The list.append() method adds an item to the end of the list.

The method returns None as it mutates the original list.

# Changing the value of the element at the last index in the list

If you meant to change the value of the last index in the list, use -1 .

When the index starts with a minus, we start counting backward from the end of the list.

# Declaring a list that contains N elements and updating a certain index

Alternatively, you can declare a list that contains N elements with None values.

The item you specify in the list will be contained N times in the new list the operation returns.

Make sure to wrap the value you want to repeat in a list.

If the list contains a value at the specific index, then you are able to change it.

# Using a try/except statement to handle the error

If you need to handle the error if the specified list index doesn't exist, use a try/except statement.

The list in the example has 3 elements, so its last element has an index of 2 .

We wrapped the assignment in a try/except block, so the IndexError is handled by the except block.

You can also use a pass statement in the except block if you need to ignore the error.

The pass statement does nothing and is used when a statement is required syntactically but the program requires no action.

# Getting the length of a list

If you need to get the length of the list, use the len() function.

The len() function returns the length (the number of items) of an object.

The argument the function takes may be a sequence (a string, tuple, list, range or bytes) or a collection (a dictionary, set, or frozen set).

If you need to check if an index exists before assigning a value, use an if statement.

This means that you can check if the list's length is greater than the index you are trying to assign to.

# Trying to assign a value to an empty list at a specific index

Note that if you try to assign to an empty list at a specific index, you'd always get an IndexError .

You should print the list you are trying to access and its length to make sure the variable stores what you expect.

# Use the extend() method to add multiple items to the end of a list

If you need to add multiple items to the end of a list, use the extend() method.

The list.extend method takes an iterable (such as a list) and extends the list by appending all of the items from the iterable.

The list.extend method returns None as it mutates the original list.

# (CSV) IndexError: list index out of range in Python

The Python CSV "IndexError: list index out of range" occurs when we try to access a list at an index out of range, e.g. an empty row in a CSV file.

To solve the error, check if the row isn't empty before accessing it at an index, or check if the index exists in the list.

Assume we have the following CSV file.

And we are trying to read it as follows.

# Check if the list contains elements before accessing it

One way to solve the error is to check if the list contains any elements before accessing it at an index.

The if statement checks if the list is truthy on each iteration.

All values that are not truthy are considered falsy. The falsy values in Python are:

• constants defined to be falsy: None and False .
• 0 (zero) of any numeric type
• empty sequences and collections: "" (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set), range(0) (empty range).

# Check if the index you are trying to access exists in the list

Alternatively, you can check whether the specific index you are trying to access exists in the list.

This means that you can check if the list's length is greater than the index you are trying to access.

# Use a try/except statement to handle the error

Alternatively, you can use a try/except block to handle the error.

We try to access the list of the current iteration at index 1 , and if an IndexError is raised, we can handle it in the except block or continue to the next iteration.

# sys.argv [1] IndexError: list index out of range in Python

The sys.argv "IndexError: list index out of range in Python" occurs when we run a Python script without specifying values for the required command line arguments.

To solve the error, provide values for the required arguments, e.g. python main.py first second .

I ran the script with python main.py .

The sys.argv list contains the command line arguments that were passed to the Python script.

# Provide all of the required command line arguments

To solve the error, make sure to provide all of the required command line arguments when running the script, e.g. python main.py first second .

Notice that the first item in the list is always the name of the script.

It is operating system dependent if this is the full pathname or not.

# Check if the sys.argv list contains the index

If you don't have to always specify all of the command line arguments that your script tries to access, use an if statement to check if the sys.argv list contains the index that you are trying to access.

I ran the script as python main.py without providing any command line arguments, so the condition wasn't met and the else block ran.

We tried accessing the list item at index 1 which raised an IndexError exception.

You can handle the error or use the pass keyword in the except block.

# IndexError: pop index out of range in Python

The Python "IndexError: pop index out of range" occurs when we pass an index that doesn't exist in the list to the pop() method.

To solve the error, pass an index that exists to the method or call the pop() method without arguments to remove the last item from the list.

The list has a length of 3 . Since indexes in Python are zero-based, the first item in the list has an index of 0 , and the last an index of 2 .

If you need to remove the last item in the list, call the method without passing it an index.

The list.pop method removes the item at the given position in the list and returns it.

You can also use negative indices to count backward, e.g. my_list.pop(-1) removes the last item of the list, and my_list.pop(-2) removes the second-to-last item.

Alternatively, you can check if an item at the specified index exists before passing it to pop() .

This means that you can check if the list's length is greater than the index you are passing to pop() .

An alternative approach to handle the error is to use a try/except block.

If calling the pop() method with the provided index raises an IndexError , the except block is run, where we can handle the error or use the pass keyword to ignore it.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• IndexError: index 0 is out of bounds for axis 0 with size 0
• IndexError: invalid index to scalar variable in Python
• IndexError: pop from empty list in Python [Solved]
• Replacement index 1 out of range for positional args tuple
• IndexError: too many indices for array in Python [Solved]
• IndexError: tuple index out of range in Python [Solved]

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Copyright © 2024 Borislav Hadzhiev

How to Fix Python IndexError: list assignment index out of range

• Python How-To's
• How to Fix Python IndexError: list …

Python IndexError: list assignment index out of range

Fix the indexerror: list assignment index out of range in python, fix indexerror: list assignment index out of range using append() function, fix indexerror: list assignment index out of range using insert() function.

In Python, the IndexError: list assignment index out of range is raised when you try to access an index of a list that doesn’t even exist. An index is the location of values inside an iterable such as a string, list, or array.

In this article, we’ll learn how to fix the Index Error list assignment index out-of-range error in Python.

Let’s see an example of the error to understand and solve it.

Code Example:

The reason behind the IndexError: list assignment index out of range in the above code is that we’re trying to access the value at the index 3 , which is not available in list j .

To fix this error, we need to adjust the indexing of iterables in this case list. Let’s say we have two lists, and you want to replace list a with list b .

You cannot assign values to list b because the length of it is 0 , and you are trying to add values at kth index b[k] = I , so it is raising the Index Error. You can fix it using the append() and insert() .

The append() function adds items (values, strings, objects, etc.) at the end of the list. It is helpful because you don’t have to manage the index headache.

The insert() function can directly insert values to the k'th position in the list. It takes two arguments, insert(index, value) .

In addition to the above two solutions, if you want to treat Python lists like normal arrays in other languages, you can pre-defined your list size with None values.

Once you have defined your list with dummy values None , you can use it accordingly.

There could be a few more manual techniques and logic to handle the IndexError: list assignment index out of range in Python. This article overviews the two common list functions that help us handle the Index Error in Python while replacing two lists.

We have also discussed an alternative solution to pre-defined the list and treat it as an array similar to the arrays of other programming languages.

Zeeshan is a detail oriented software engineer that helps companies and individuals make their lives and easier with software solutions.

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How to Fix “IndexError: List Assignment Index Out of Range” in Python

Table of Contents

The IndexError: List Assignment Index Out of Range error occurs when you assign a value to an index that is beyond the valid range of indices in the list. As Python uses zero-based indexing, when you try to access an element at an index less than 0 or greater than or equal to the list’s length, you trigger this error.

It’s not as complicated as it sounds. Think of it this way: you have a row of ten mailboxes, numbered from 0 to 9. These mailboxes represent the list in Python. Now, if you try to put a letter into mailbox number 10, which doesn't exist, you'll face a problem. Similarly, if you try to put a letter into any negative number mailbox, you'll face the same issue because those mailboxes don't exist either.

The IndexError: List Assignment Index Out of Range error in Python is like trying to put a letter into a mailbox that doesn't exist in our row of mailboxes. Just as you can't access a non-existent mailbox, you can't assign a value to an index in a list that doesn't exist.

Let’s take a look at example code that raises this error and some strategies to prevent it from occurring in the first place.

Example of “IndexError: List Assignment Index Out of Range”

Remember, assigning a value at an index that is negative or out of bounds of the valid range of indices of the list raises the error.

How to resolve “IndexError: List Assignment Index Out of Range”

You can use methods such as append() or insert() to insert a new element into the list.

How to use the append() method

Use the append() method to add elements to extend the list properly and avoid out-of-range assignments.

How to use the insert() method

Use the insert() method to insert elements at a specific position instead of direct assignment to avoid out-of-range assignments.

Now one big advantage of using insert() is even if you specify an index position which is way out of range it won’t give any error and it will just append the element at the end of the list.

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Related Resources

How to Handle TypeError: Cannot Unpack Non-iterable Nonetype Objects in Python

How to Fix IndexError: string index out of range in Python

How to Fix Python’s “List Index Out of Range” Error in For Loops

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Python indexerror: list assignment index out of range Solution

An IndexError is nothing to worry about. It’s an error that is raised when you try to access an index that is outside of the size of a list. How do you solve this issue? Where can it be raised?

In this article, we’re going to answer those questions. We will discuss what IndexErrors are and how you can solve the “list assignment index out of range” error. We’ll walk through an example to help you see exactly what causes this error.

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Without further ado, let’s begin!

The Problem: indexerror: list assignment index out of range

When you receive an error message, the first thing you should do is read it. An error message can tell you a lot about the nature of an error.

Our error message is: indexerror: list assignment index out of range.

IndexError tells us that there is a problem with how we are accessing an index . An index is a value inside an iterable object, such as a list or a string.

The message “list assignment index out of range” tells us that we are trying to assign an item to an index that does not exist.

In order to use indexing on a list, you need to initialize the list. If you try to assign an item into a list at an index position that does not exist, this error will be raised.

An Example Scenario

The list assignment error is commonly raised in for and while loops .

We’re going to write a program that adds all the cakes containing the word “Strawberry” into a new array. Let’s start by declaring two variables:

The first variable stores our list of cakes. The second variable is an empty list that will store all of the strawberry cakes. Next, we’re going to write a loop that checks if each value in “cakes” contains the word “Strawberry”.

If a value contains “Strawberry”, it should be added to our new array. Otherwise, nothing will happen. Once our for loop has executed, the “strawberry” array should be printed to the console. Let’s run our code and see what happens:

As we expected, an error has been raised. Now we get to solve it!

The Solution

Our error message tells us the line of code at which our program fails:

The problem with this code is that we are trying to assign a value inside our “strawberry” list to a position that does not exist.

When we create our strawberry array, it has no values. This means that it has no index numbers. The following values do not exist:

We are trying to assign values to these positions in our for loop. Because these positions contain no values, an error is returned.

We can solve this problem in two ways.

Solution with append()

First, we can add an item to the “strawberry” array using append() :

The append() method adds an item to an array and creates an index position for that item. Let’s run our code: [‘Strawberry Tart’, ‘Strawberry Cheesecake’].

Our code works!

Solution with Initializing an Array

Alternatively, we can initialize our array with some values when we declare it. This will create the index positions at which we can store values inside our “strawberry” array.

To initialize an array, you can use this code:

This will create an array with 10 empty values. Our code now looks like this:

Let’s try to run our code:

Our code successfully returns an array with all the strawberry cakes.

This method is best to use when you know exactly how many values you’re going to store in an array.

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Our above code is somewhat inefficient because we have initialized “strawberry” with 10 empty values. There are only a total of three cakes in our “cakes” array that could possibly contain “Strawberry”. In most cases, using the append() method is both more elegant and more efficient.

IndexErrors are raised when you try to use an item at an index value that does not exist. The “indexerror: list assignment index out of range” is raised when you try to assign an item to an index position that does not exist.

To solve this error, you can use append() to add an item to a list. You can also initialize a list before you start inserting values to avoid this error.

Now you’re ready to start solving the list assignment error like a professional Python developer!

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Resolve "index out of range" errors

As a Python developer, working with lists is an essential part of your daily coding routine. However, even experienced programmers can stumble upon the dreaded “index out of range” error when dealing with list assignments. This error occurs when you attempt to access or modify an index that doesn’t exist within the list’s bounds. Fear not, as this comprehensive tutorial will equip you with the knowledge and techniques to conquer this challenge and unlock the full potential of Python’s list assignment.

Understanding the “Index Out of Range” Error

Before diving into the solutions, let’s first understand the root cause of the “index out of range” error. In Python, lists are zero-indexed, meaning the first element has an index of 0, the second element has an index of 1, and so on. When you try to access or modify an index that falls outside the list’s valid range, Python raises an IndexError with the “index out of range” message.

Here’s an example that illustrates the error:

In this case, we’re attempting to access the fourth element ( my_list[3] ) of a list that only contains three elements (indices 0, 1, and 2).

Solution 1: Validating Indices Before Assignment

One effective solution to prevent “index out of range” errors is to validate the index before attempting to assign a value to it. You can achieve this by checking if the index falls within the list’s valid range using the len() function and conditional statements.

In this solution, we first declare a list my_list with three elements. We then define two variables: index and new_value .

Next, we use an if statement to check if the index is less than the length of my_list . The len(my_list) function returns the number of elements in the list, which is 3 in this case.

If the condition index < len(my_list) is True, it means that the index is a valid index within the list’s bounds. In this case, we assign the new_value (4) to the element at the specified index (2) using the list assignment my_list[index] = new_value . Finally, we print the updated list, which now has the value 4 at index 2.

However, if the condition index < len(my_list) is False, it means that the index is out of range for the given list. In this case, we execute the else block and print the message “Index out of range!” to inform the user that the provided index is invalid.

This solution is effective when you need to ensure that the index you’re trying to access or modify is within the valid range of the list. By checking the index against the list’s length , you can prevent “index out of range” errors and handle invalid indices appropriately.

It’s important to note that this solution assumes that the index variable is provided or calculated elsewhere in the code. In a real-world scenario, you may need to handle user input or perform additional validation on the index variable to ensure it’s an integer and within the expected range.

Solution 2: Using Python’s List Slicing

Python’s list slicing feature allows you to access and modify a subset of elements within a list. This is a powerful technique that can help you avoid “index out of range” errors when working with list assignments .

In the first example, my_list[:2] = [10, 20] , we’re using list slicing to access and modify the elements from the start of the list up to (but not including) index 2. The slice [:2] represents the range from the beginning of the list to index 2 (0 and 1). We then assign the new values [10, 20] to this slice, effectively replacing the original values at indices 0 and 1 with 10 and 20, respectively.

In the second example, my_list[2:] = [30, 40] , we’re using list slicing to access and modify the elements from index 2 to the end of the list. The slice [2:] represents the range from index 2 to the end of the list. We then assign the new values [30, 40] to this slice. Since the original list only had three elements, Python automatically extends the list by adding a new element at index 3 to accommodate the second value (40).

List slicing is a powerful technique because it allows you to modify multiple elements within a list without worrying about “index out of range” errors. Python automatically handles the indices for you, ensuring that the assignment operation is performed within the valid range of the list.

Here are a few key points about list slicing:

• Inclusive start, exclusive end : The slice [start:end] includes the elements from start up to, but not including, end .
• Omitting start or end : If you omit the start index, Python assumes the beginning of the list. If you omit the end index, Python assumes the end of the list.
• Negative indices : You can use negative indices to start or end the slice from the end of the list. For example, my_list[-1] accesses the last element of the list.
• Step size : You can optionally specify a step size in the slice notation, e.g., my_list[::2] to access every other element of the list.

List slicing is a powerful and Pythonic way to work with lists, and it can help you avoid “index out of range” errors when assigning values to multiple elements within a list.

Solution 3: Using Python’s List Append Method

The append() method in Python is a built-in list method that allows you to add a new element to the end of an existing list. This method is particularly useful when you want to avoid “index out of range” errors that can occur when trying to assign a value to an index that doesn’t exist in the list.

In this example, we start with a list my_list containing three elements: [1, 2, 3] . We then use the append() method to add a new element 4 to the end of the list: my_list.append(4) . Finally, we print the updated list, which now contains four elements: [1, 2, 3, 4] .

Here’s how the append() method works:

• Python finds the current length of the list using len(my_list) .
• It assigns the new value ( 4 in this case) to the index len(my_list) , which is the next available index after the last element in the list.
• Since the new index is always valid (it’s one greater than the last index), there’s no risk of an “index out of range” error.

The append() method is a safe and convenient way to add new elements to the end of a list because it automatically handles the index assignment for you. You don’t need to worry about calculating the correct index or checking if the index is within the list’s bounds.

It’s important to note that the append() method modifies the original list in-place. If you want to create a new list instead of modifying the existing one, you can use the + operator or the list.copy() method to create a copy of the list first, and then append the new element to the copy.

Another advantage of using append() is that it allows you to add multiple elements to the list in a loop or by iterating over another sequence. For example:

In this example, we use a for loop to iterate over the new_elements list, and for each element, we call my_list.append(element) to add it to the end of my_list .

Overall, the append() method is a simple and effective way to add new elements to the end of a list, ensuring that you avoid “index out of range” errors while maintaining the integrity and order of your list.

Solution 4: Handling Exceptions with Try/Except Blocks

Python provides a robust exception handling mechanism using try/except blocks, which can be used to gracefully handle “index out of range” errors and other exceptions that may occur during program execution.

In this example, we first define a list my_list with three elements and an index variable with the value 4 .

The try block contains the code that might raise an exception. In this case, we attempt to access the element at my_list[index] , which is my_list[4] . Since the list only has indices from 0 to 2, this operation will raise an IndexError with the message “list index out of range” .

The except block specifies the type of exception to catch, which is IndexError in this case. If an IndexError is raised within the try block, the code inside the except block will be executed. Here, we print the message “Index out of range! Please provide a valid index.” to inform the user that the provided index is invalid.

If no exception is raised within the try block, the except block is skipped, and the program continues executing the code after the try/except block.

By using try/except blocks, you can handle exceptions gracefully and provide appropriate error messages or take alternative actions, rather than allowing the program to crash with an unhandled exception.

Here are a few key points about using try/except blocks for handling exceptions:

• Multiple except blocks : You can have multiple except blocks to handle different types of exceptions. This allows you to provide specific error handling for each exception type.
• Exception objects : The except block can optionally include a variable to hold the exception object, which can provide additional information about the exception.
• else clause : You can include an else clause after the except blocks. The else block executes if no exceptions are raised in the try block.
• finally clause : The finally clause is executed regardless of whether an exception was raised or not. It’s typically used for cleanup operations, such as closing files or releasing resources.
• Exception hierarchy : Python has a built-in exception hierarchy, where some exceptions are derived from others. You can catch a base exception to handle multiple related exceptions or catch specific exceptions for more granular control.

By using try/except blocks and handling exceptions properly, you can write more robust and resilient code that gracefully handles errors, making it easier to debug and maintain your Python programs.

Best Practices and Coding Standards

To ensure your code is not only functional but also maintainable and scalable, it’s essential to follow best practices and coding standards. Here are some recommendations:

• Validate user input : When working with user-provided indices, always validate the input to ensure it falls within the list’s valid range.
• Use descriptive variable and function names : Choose meaningful names that clearly convey the purpose and functionality of your code elements.
• Write clear and concise comments : Document your code with comments that explain the purpose, logic, and any non-obvious implementation details.
• Follow PEP 8 style guide : Adhere to Python’s official style guide , PEP 8, to ensure consistency and readability across your codebase.
• Test your code thoroughly : Implement unit tests and integrate testing into your development workflow to catch bugs and regressions early.

By following these best practices and coding standards, you’ll not only avoid “index out of range” errors but also produce high-quality, maintainable, and scalable Python code.

Mastering Python’s list assignment is crucial for efficient data manipulation and programming success. By understanding the root cause of “index out of range” errors and implementing the solutions outlined in this tutorial, you’ll be well-equipped to handle these challenges confidently. Whether you validate indices, leverage list slicing, use the append() method, or handle exceptions, you now have a comprehensive toolkit to tackle list assignment challenges head-on. Embrace these techniques, follow best practices, and continue honing your Python skills to unlock new levels of coding excellence.

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List Index Out of Range – Python Error [Solved]

In this article, we'll talk about the IndexError: list index out of range error in Python.

In each section of the article, I'll highlight a possible cause for the error and how to fix it.

You may get the IndexError: list index out of range error for the following reasons:

• Trying to access an index that doesn't exist in a list.
• Using invalid indexes in your loops.
• Specifying a range that exceeds the indexes in a list when using the range() function.

Before we proceed to fixing the error, let's discuss how indexing work in Python lists. You can skip the next section if you already know how indexing works.

How Does Indexing Work in Python Lists?

Each item in a Python list can be assessed using its index number. The first item in a list has an index of zero.

Consider the list below:

In the example above, we have a list called languages . The list has three items — 'Python', 'JavaScript', and 'Java'.

To access the second item, we used its index: languages[1] . This printed out JavaScript .

Some beginners might misunderstand this. They may assume that since the index is 1, it should be the first item.

To make it easier to understand, here's a breakdown of the items in the list according to their indexes:

Python (item 1) => Index 0 JavaScript (item 2) => Index 1 Java (item 3) => Index 2

As you can see above, the first item has an index of 0 (because Python is "zero-indexed"). To access items in a list, you make use of their indexes.

What Will Happen If You Try to Use an Index That Is Out of Range in a Python List?

If you try to access an item in a list using an index that is out of range, you'll get the IndexError: list index out of range error.

Here's an example:

In the example above, we tried to access a fourth item using its index: languages[3] . We got the IndexError: list index out of range error because the list has no fourth item – it has only three items.

The easy fix is to always use an index that exists in a list when trying to access items in the list.

How to Fix the IndexError: list index out of range Error in Python Loops

Loops work with conditions. So, until a certain condition is met, they'll keep running.

In the example below, we'll try to print all the items in a list using a while loop.

The code above returns the   IndexError: list index out of range error. Let's break down the code to understand why this happened.

First, we initialized a variable i and gave it a value of 0: i = 0 .

We then gave a condition for a while loop (this is what causes the error):   while i <= len(languages) .

From the condition given, we're saying, "this loop should keep running as long as i is less than or equal to the length of the language list".

The len() function returns the length of the list. In our case, 3 will be returned. So the condition will be this: while i <= 3 . The loop will stop when i is equal to 3.

Let's pretend to be the Python compiler. Here's what happens as the loop runs.

Here's the list: languages = ['Python', 'JavaScript', 'Java'] . It has three indexes — 0, 1, and 2.

When i is 0 => Python

When i is 1 => JavaScript

When i is 2 => Java

When i is 3 => Index not found in the list. IndexError: list index out of range error thrown.

So the error is thrown when i is equal to 3 because there is no item with an index of 3 in the list.

To fix this problem, we can modify the condition of the loop by removing the equal to sign. This will stop the loop once it gets to the last index.

Here's how:

The condition now looks like this: while i < 3 .

The loop will stop at 2 because the condition doesn't allow it to equate to the value returned by the len() function.

How to Fix the IndexError: list index out of range Error in When Using the range() Function in Python

By default, the range() function returns a "range" of specified numbers starting from zero.

Here's an example of the range() function in use:

As you can see in the example above, range(5) returns 0, 1, 2, 3, 4.

You can use the range() function with a loop to print the items in a list.

The first example will show a code block that throws the   IndexError: list index out of range error. After pointing out why the error occurred, we'll fix it.

The example above prints all the items in the list along with the IndexError: list index out of range error.

We got the error because range(4) returns 0, 1, 2, 3. Our list has no index with the value of 3.

To fix this, you can modify the parameter in the range() function. A better solution is to use the length of the list as the range() function's parameter.

The code above runs without any error because the len() function returns 3. Using that with range(3) returns 0, 1, 2 which matches the number of items in a list.

In this article, we talked about the   IndexError: list index out of range error in Python.

This error generally occurs when we try to access an item in a list by using an index that doesn't exist within the list.

We saw some examples that showed how we may get the error when working with loops, the len() function, and the range() function.

We also saw how to fix the IndexError: list index out of range error for each case.

Happy coding!

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Python Indexerror: list assignment index out of range Solution

In python, lists are mutable as the elements of a list can be modified. But if you try to modify a value whose index is greater than or equal to the length of the list then you will encounter an Indexerror: list assignment index out of range.  

Python Indexerror: list assignment index out of range Example

If ‘fruits’ is a list, fruits=[‘Apple’,’ Banana’,’ Guava’]and you try to modify fruits[5] then you will get an index error since the length of fruits list=3 which is less than index asked to modify for which is 5.

So, as you can see in the above example, we get an error when we try to modify an index that is not present in the list of fruits.

Method 1: Using insert() function

The insert(index, element) function takes two arguments, index and element, and adds a new element at the specified index.

Let’s see how you can add Mango to the list of fruits on index 1.

It is necessary to specify the index in the insert(index, element) function, otherwise, you will an error that the insert(index, element) function needed two arguments.

Method 2: Using append()

The append(element) function takes one argument element and adds a new element at the end of the list.

Let’s see how you can add Mango to the end of the list using the append(element) function.

Python IndexError FAQ

Q: what is an indexerror in python.

A: An IndexError is a common error that occurs when you try to access an element in a list, tuple, or other sequence using an index that is out of range. It means that the index you provided is either negative or greater than or equal to the length of the sequence.

Q: How can I fix an IndexError in Python?

A: To fix an IndexError, you can take the following steps:

• Check the index value: Make sure the index you’re using is within the valid range for the sequence. Remember that indexing starts from 0, so the first element is at index 0, the second at index 1, and so on.
• Verify the sequence length: Ensure that the sequence you’re working with has enough elements. If the sequence is empty, trying to access any index will result in an IndexError.
• Review loop conditions: If the IndexError occurs within a loop, check the loop conditions to ensure they are correctly set. Make sure the loop is not running more times than expected or trying to access an element beyond the sequence’s length.
• Use try-except: Wrap the code block that might raise an IndexError within a try-except block. This allows you to catch the exception and handle it gracefully, preventing your program from crashing.

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For Beginners

Pygame errror: indexerror: list index out of range.

Crazylegs830

Hello, I was just making a "Stickman" class for the player and I get this error :IndexError: list index out of range

Here is the code:

DejaimeNeto

It looks like you're going over the end of a list, but I really can't understand what your code is doing (no experience with python).

From this line, I assume self.ani has only one record (the name of the file).

But here, it looks like you're trying to read other positions from self.ani that currently doesn't exist.

So, maybe if you changed this last line to the code below, it would stop going over the end of the list (stay on the only record in it)

I probably don't know what I'm talking about since I know nothing about python.

It looks like you're going over the end of a list, but I really can't understand what your code is doing (no experience with python). From this line, I assume self.ani has only one record (the name of the file). self.ani = glob.glob("C:\Users\user\Desktop\Python Programs\Sprite Example\Entities\Stcik_Man_Walk*.png") But here, it looks like you're trying to read other positions from self.ani that currently doesn't exist. self.img = pygame.image.load(self.ani[self.ani_pos]) So, maybe if you changed this last line to the code below, it would stop going over the end of the list (stay on the only record in it) self.img = pygame.image.load(self.ani[0]) I probably don't know what I'm talking about since I know nothing about python.

I fixed it now was a simple misspell error.

KnolanCross

It is complaining that you tried to access an element that doesn't exist in an list.

In the stack trace it will show you exactly where is the problem, but - unless it is an internal pygame call - the only points that it can be are here:

You can either use pdb to debug it or print those lists to check what is inside and how many elements they have.

Currently working on a scene editor for ORX ( http://orx-project.org ), using kivy ( http://kivy.org ).

This topic is closed to new replies.

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List index out of range error.

Hey, i need help with this error i'm getting in my code for no apparent reason on line 37 and line 31 for moving left and right respectively

EDIT: the whole error

File "C:/Users/####/.PyCharmCE2018.2/config/scratches/scratch_4.py", line 37, in update

self.image = self.images[self.frame//ani]

IndexError: list index out of range

just deleted the line self.image = self.images[self.frame//ani] and it worked

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How to fix "IndexError: list assignment index out of range" error in Python?

I'm a beginner to Python with very little experience in coding. I've started writing a Python program to multiply two matrices. The following code gives me output for square matrices but gives me the following error when I enter, say for example, m=2, n=3, p=3, q=2:

Could anybody please help me out with this? Thank you!

HERE'S THE CODE:

strong text

• 1 You have your rows and columns mixed up. You have m columns and n rows. –  Mark Commented Jan 8, 2019 at 19:23
• You have your indexes in wrong order, it should be a[j][i] = (int(input())) , same for rest of your code. –  Filip Młynarski Commented Jan 8, 2019 at 19:23
• The problem is in matrix initialization step with list comprehension. The original matrix itself is contained within a list, so it is a 3D list. –  Endyd Commented Jan 8, 2019 at 19:26

3 Answers 3

A couple of trivial tracing statements helped find the problem: your dimension limits are switched. Try this:

See this lovely debug blog for help.

Your matrix definition for a , b , and c are producing a 3D matrix instead of your desired 2D matrix with rows and columns.

Put a placeholder value of 0 in each cell of the matrix as such:

resulting matrix shape for 2x3 a and 3x4

Put an empty list for each row of the matrix, and append columns to each row.

Resulting matrix is a list containing row-number of empty lists.

Then you want to append instead of indexing for matrix[i][j] since columns don't yet exist.

I just Post the Complete Solution. you can read @Endyd Answer for the Explanation.

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ai_gym list assignment index out of range #14064

Chxinnn commented Jun 28, 2024 • edited by ambitious-octopus Loading

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